Zr-Ti-Ni (Cu) based brazing filler alloy compositions with lower melting point for the brazing of titanium alloys

ABSTRACT

Disclosed is Zr—Ti—Ni(Cu)-based filler alloy composition having low melting point for brazing titanium and titanium alloys. The Zr—Ti—Ni(Cu)-based alloy composition is expressed as: Zr a Ti b Ni c  (Formula 1) where a, b and c denote atomic % of Zr, Ti and Ni, respectively; 47≦a≦52; 24≦b≦30; 22≦c≦26; and 0.3&lt;c/(a+c)&lt;0.35, or Zr a Ti b Ni c Cu d  (Formula 2) where a, b, c and d denote atomic % of Zr, Ti, Ni and Cu respectively; 48≦a≦60; 20≦b≦28; 19≦c+d≦30; 3≦d≦12; and 0.12&lt;d/(c+d)≦0.5. Including Zr(Ti) solid solution phase as its major constituent phase, the alloy compositions of this invention have lower liquidus temperature than those of conventional alloys and they include a little amount of Cu or does not include it at all. When alloy of the present invention is used as filler alloy for brazing titanium and titanium alloys, brazing can be performed at remarkably low temperature. This prevents the microstructure of titanium base metal from changing and being damaged, keeping the titanium base metal preserving inherent properties after brazing.

TECHNICAL FIELD

The present invention relates to a filler alloy composition for brazing titanium which has a low melting point; and, more particularly, in case of brazing of Ti, Ti alloys or dissimilar materials including titanium or titanium alloy, brazing with this alloy can provide a robust joint body and preserve mechanical properties of titanium base metal after brazing process.

BACKGROUND ART

Many filler alloys have been developed and researched for brazing titanium and titanium alloy. The developed Filler alloys are largely divided into four groups: aluminum (Al)-based filler alloy, silver (Ag)-based filler alloy, titanium (Ti)-based filler alloy, and zirconium (Zr)-based filler alloy. In case of using the Al-based filler alloy and Ag-based filler alloy, a detrimental intermetallic compound phase is formed by reactions between the major elements comprising the filler metals and Ti base alloys in Ti brazed joint area. Thus, they are improper for the formation of a robust Ti joint body which requires heat-resistance, corrosion resistance, strength and reliability. On the contrary, active-element based filler alloys, containing large amount of active elements such as Ti and Zr element have been well known to provide a good Ti brazed joint body having excellent heat-resistance corrosion resistance and strength at room temperature and high temperature. However, since the active element-based filler alloys have relatively high melting points, their brazing temperature can be close to the recrystallization temperature and beta transus temperature of titanium base metals to be joined. So the microstructure of Ti base metal may be altered if the brazing temperature exceeds these restrictive temperatures. Eventually, the change of original microstructure of Ti-based alloy after brazing causes the mechanical properties of base metal to be impaired.

When brazing (α+β) type and β type Ti alloys, there has been actual restriction in selecting a brazing cycle and a filler alloy with a low melting point that can allow heat-treated (α+β) type and β type Ti alloys to braze without changing their heated structure. Theoretically, it is desirable that Ti-based alloy should be brazed at a temperature as lower as from 55 to 83° C. than its beta transus temperature. If Ti alloy is brazed at a temperature higher than the restrictive temperatures, the mechanical properties such as strength and ductility particular in the α+β type and β type Ti alloys heat-treated may be impaired. The damaged mechanical properties of Ti base metals are hard to be recovered without another heat treatment for the brazed assembly. After brazing, the re-heat treatment of brazed part such as quenching may deform the brazed assembly in large size with complicated shape due to the rapid change in the temperature. Therefore, post heat treatment of the brazed assembly after brazing is not preferable to solve this problem.

In order to reduce the impairment of Ti base metal after brazing, using filler alloy with low melting point has been preferable as an effective method. With the active element based filler alloys developed, their brazing temperature has to be set at temperature more than 850° C. This is because a conventional filler alloy having the lowest melting point has a liquidus temperature of approximately 843° C. at Ti-37.5Zr-15Cu-10Ni in wt % (Ti_(48.5)Zr_(25.7)Cu_(14.8)Ni_(10.6) in atomic %). In case of beryllium (Be) containing active brazing filler alloys such as Zr—Ti—Ni—Be have a liquidus temperature less than 800° C. because Be element is a strong melting point depressant of Ti and Zr. However, the use of Zr—Ti—Ni—Be has been restricted since Be is a hazardous element. Also, another Zr-based filler alloy in free of Be, which is Zr-11Ti-14Ni-13Cu (wt %) (Zr_(50.3)Ti_(17.0)Cu_(15.1)Ni_(17.6) in atomic %), has a liquidus temperature about at 830° C. Even though its liquidus temperature is lower than that of other Ti-based filler alloys by approximately 20˜30° C., but it has a drawback that brazing should be performed at a high temperature more than 900° C.

Also, conventional filler alloys taking an active element, e.g., Ti or Zr, as a base includes copper (Cu) and/or nickel (Ni) more than 14% by atomic ratio as a melting point depressant. Herein, although Cu is effective in drastically dropping the melting point of an alloy in the presence of Ni, it has a shortcoming that it also deteriorates mechanical and chemical properties of the brazing joint body when it is included abundantly. In short, Cu causes a brittle intermetallic compound to be generated easily during a joining process and a process of cooling a joint body.

According to a study by Botztein et al published in Materials Science and Engineering A, Vol. 206, pp. 14-23, 1995, when a Ti alloy is brazed using a Cu—Ti—Zr filler alloy, a brittle λ-Cu₂TiZr Lavas phase appears during slow cooling process. To prevent the formation of the brittle phase, it is recommended to limit the Cu concentration in the joint body to go not more than approximately 10 wt % to approximately 12 wt %.

Also, a study by Chang et al published in Journal of Materials Engineering and Performance, Vol. 6(6), pp. 797-803, 1997, reveals that when Ti-6Al-4V is joined at approximately 960° C. using Ti-21Ni-14Cu molten filler in a joint body reacts with an (α+β)-type Ti-based alloy to thereby form a lamellar-type Widmanstatten structure consisting of a Ti₂Ni phase and a Ti₂Cu phase. Herein, the Ti₂Ni phase disappears as Ni component existing on a joint body in the initial state diffuses into the inside of a base metal during a 2-hour-long diffusion process. On the other hand, the Ti₂Cu phase still remains on the joint body.

In consequences, the high melting temperature of conventional filler alloys and a high content of Cu have been pointed out as factors degrading durability of a Ti-brazed assembly. Therefore, when Ti alloy is brazed using typical filler alloy, a short brazing cycle is needed in order to protect base metal from being mechanically damaged. To be specific, the Ti alloy should be heated up to quickly reach as high brazing temperature as approximately 850° C. and up, maintained at the brazing temperature for a short time no longer than approximately 15 minutes, and quenched rapidly. The short brazing cycle may be disadvantageous when a metal like Ti having heat conductivity lower than other metals is used for a joint body.

To sum up, it is necessary to limit the amount of Cu added to a filler alloy to a minimum amount in developing new active element-based filler alloy having a low melting point.

DISCLOSURE Technical Problem

An embodiment of the present invention devised to overcome the above problems is directed to providing a filler alloy composition having a low melting point that can be brazed at a temperature lower than conventional brazing temperature to preserve mechanical properties of a Ti-based metal during a heat cycle and form a robust joint body, when Ti, Ti alloy or dissimilar material joining including Ti or Ti alloy is brazed to be assembled.

Particularly, an embodiment of the present invention is directed to providing a filler alloy composition which does not include an element hazardous to a human body, such as Be, has a melting point much lower than typical active element-based filter alloy so that brazing can be performed at a temperature lower than approximately 800° C., and includes Cu element, which may degrade mechanical and chemical properties of a joint body, within a range of approximately 12 atomic % or does not include Cu at all.

Technical Solution

In accordance with an aspect of the present invention, there is provided a Zr—Ti—Ni ternary alloy composition, expressed as: Zr_(a)Ti_(b)Ni_(c)  Formula 1

where a, b and c denote atomic % of Zr, Ti and Ni, respectively; 47≦a≦52; 24≦b≦30; 22≦c≦26; and 0.3<c/(a+c)<0.35.

In accordance with another aspect of the present invention, there is provided a Zr—Ti—Ni—Cu quaternary alloy composition, expressed as: Zr_(a)Ti_(b)Ni_(c)Cu_(d)  Formula 2

where a, b, c and d denote atomic % of Zr, Ti, Ni and Cu respectively; 48≦a≦60; 20≦b≦28; 19≦c+d≦30; 3≦d≦12; and 0.12<d/(c+d) 0.5.

Advantageous Effects

The Zr—Ti—Ni ternary filer alloy compositions have a constituent phase of Zr(Ti) solid solution phase, (Zr,Ti)₂Ni phase, and Zr₂Ni phase at room temperature after slow solidification, and the filler alloys can have low melting temperature ranging approximately 797° C. to approximately 825° C. upon heating through eutectic reaction between the phases. Also, the Zr—Ti—Ni—Cu quaternary filer alloy compositions have a constituent phase of Zr(Ti) solid solution phase with Cu dissolved therein, (Zr,Ti)₂Ni phase with Cu dissolved therein, and Zr₂Ni phase with Cu dissolved therein at room temperature, or it may have a constituent phase of Zr(Ti) solid solution phase with Cu dissolved therein, (Zr,Ti)₂Ni phase with Cu dissolved therein, and Zr₂Cu phase with Ni dissolved therein to thereby have a low melting point not higher than approximately 772° C. to approximately 809° C. Furthermore, the total Cu content in the Zr—Ti—Ni—Cu quaternary filer alloy composition ranges from approximately 3 atomic % to approximately 12 atomic %, and the amount of Cu in the Ni+Cu obtained by aggregating the Ni content and the Cu content does not exceed approximately 50 atomic %. In short, the Ni content is equal to or greater than the Cu content.

Therefore, the filler alloy compositions of the present invention have a lower brazing temperature than those of conventional filler alloys, it can be brazed at a temperature not higher than approximately 800° C. and thus it can minimize the damage on the mechanical properties of Ti-based alloy caused by phase change or grain growth of the Ti-based metal. In short, the use of the filler alloy composition of the present invention having a low melting point can minimize the extent of degradation in the strength of Ti base metal caused by a brazing heat cycle and maximize joining strength.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a composition range of a Zr—Ti—Ni ternary alloy composition in accordance with an embodiment of the present invention.

FIG. 2 shows a composition range of a Zr—Ti—Ni—Cu quaternary alloy composition in accordance with an embodiment of the present invention.

FIG. 3 is a ternary phase diagram of Zr—Ti—Ni system at 700° C.

FIG. 4 is a pseudo binary Zr₂Ni—Ti₂Ni phase diagram.

FIG. 5 is a DTA curve of Zr₅₀Ti₂₆Ni₂₄ alloy composition of Example 6 according to a first Experimental Example during heating and cooling processes.

FIG. 6 is a DTA curve of Zr₅₄Ti₂₂Ni₁₆Cu₈ alloy composition of Example 39 according to a third Experimental Example during heating and cooling processes.

FIG. 7 shows scanning electron microscopic (SEM) images showing Zr₅₀Ti₂₆Ni₂₄ alloy composition prepared according to Example 6 and Zr_(43.9)Ti_(22.8)Ni_(33.3) alloy composition prepared according to Comparative Example 8, respectively, according to Experimental Example 2.

FIG. 8 is a SEM image of Zr₅₄Ti₂₂Ni₁₆Cu₈ alloy composition of Example 39 according to Experimental Example 4.

FIG. 9 is a graph showing an X-ray Diffraction (XRD) analysis result of Zr₅₀Ti₂₆Ni₂₄ alloy composition of Example 6 prepared through melt-spinning according to Experimental Example 5.

FIG. 10 is an XRD analysis result of Zr₅₄Ti₂₂Ni₁₆Cu₈ alloy composition of Example 39 prepared through melt-spinning according to Experimental Example 5.

FIG. 11 is a graph showing tensile strengths of a base metal and a joint body using an alloy composition according to Experimental Example 6 at room temperature.

BEST MODE FOR THE INVENTION

Zr—Ti—Ni ternary alloy composition of the present invention is expressed as the following Formula 1: Zr_(a)Ti_(b)Ni_(c)  Formula 1

where a, b and c denote atomic % of Zr, Ti and Ni respectively; and 47≦a≦52, 24≦b≦30, 22≦c≦26, and 0.3<c/(a+c)<0.35.

FIG. 1 shows a composition range of a Zr—Ti—Ni ternary alloy composition in accordance with an embodiment of the present invention.

Also, Zr—Ti—Ni—Cu quaternary alloy composition of the present invention is expressed as the following Formula 2: Zr_(a)Ti_(b)Ni_(c)Cu_(d)  Formula 2

where a, b, c and d denote atomic % of Zr, Ti, Ni and Cu, respectively; and 48≦a≦60, 20≦b≦28, and 19≦c+d≦30, 3≦d≦12, and 0.12<d/(c+d)≦0.5.

FIG. 2 shows a composition range of a Zr—Ti—Ni—Cu quaternary alloy composition in accordance with an embodiment of the present invention.

As shown in FIGS. 5 and 6, Zr—Ti—Ni ternary composition or Zr—Ti—Ni—Cu quaternary alloy composition of the present invention goes through melting and solidification in a narrow temperature range during heating and cooling. To be specific, the Zr—Ti—Ni ternary alloy composition of the present invention has a solidus temperature lower than approximately 800° C. Specifically, the solidus temperature ranges from approximately 797° C. to approximately 798° C. The liquidus temperature is not higher than approximately 825° C. At the liquidus approximately, melting is completed. Specifically, the liquidus temperature ranges from approximately 809° C. to approximately 825° C. Also, the Zr—Ti—Ni—Cu quaternary alloy of the present invention has a solidus temperature lower than approximately 800° C. Specifically, the solidus temperature ranges from approximately 772° C. to approximately 792° C. The liquidus temperature is not higher than 809° C. Specifically, the liquidus temperature ranges from approximately 783° C. to approximately 809° C. As described above, the ternary and quaternary alloy compositions of the present invention have a narrow melting temperature range and a low melting point.

The low melting point is a characteristic of the Zr—Ti—Ni ternary alloy or Zr—Ti—Ni—Cu quaternary alloy suggested in the present invention and originates from a eutectic reaction among constituent phases constituting the composition.

As shown in FIGS. 3 and 4, when a Zr—Ti—Ni ternary alloy contains Ni in a uniform content of approximately 33.3 at %, the constituent phase in the Zr-rich region includes Zr₂Ni phase and (Zr,Ti)₂Ni phase, and it is known that there is a pseudo binary eutectic point of Zr₂Ni—(Zr,Ti)₂Ni of approximately 850° C. based on a eutectic reaction between the two phases.

The present invention in a Zr-based Zr—Ti—Ni alloy limits the Ni content to less than approximately 30 at %, specifically, to approximately 22 at % to approximately 26 at % to thereby form Zr solid solution phase as a new constituent phase other than the two phases. In short, as shown in FIG. 3, the ternary alloy composition range of the present invention is formed in an inverse triangle region including three types of phases: Zr₂Ni phase (body-centered tetragonal, bct), (Zr,Ti)₂Ni phase (hexagonal close-packed, hcp), and Zr(Ti) solid solution phase (hcp). A eutectic system including the three types of constituent phases comes to have a eutectic temperature lower than the eutectic temperature of the pseudo binary eutectic system and thus it is understood that the ternary alloy composition of the present invention comes to have the lower melting temperature. To be specific, the ternary alloy composition of the present invention can have a low melting temperature ranging from approximately 797° C. to approximately 825° C. through a eutectic reaction of Zr₂Ni+(Zr,Ti)₂Ni+Zr(Ti)→L during heating. Thus, it is understood that the ternary eutectic system of the present invention appears by reducing the content of Ni by less than approximately 30 at % from the composition of the pseudo binary eutectic system.

The present invention also provides a quaternary alloy composition obtained by adding Cu to the Zr—Ti—Ni ternary alloy as a melting point depressant and limiting the Cu content to approximately 3 at % to 12 at %. The quaternary alloy of the present invention can have solidus and liquidus temperature lower than the ternary alloy composition by substituting part of Ni of the ternary alloy composition with Cu, that is, by adding Cu in an amount less than or equal to the amount of the remaining Ni (Ni content≧Cu content). To be specific, the quaternary alloy composition of the present invention has a melting point as low as approximately 772° C. to approximately 809° C. through a eutectic reaction. The quaternary alloy composition can have a wider composition range including the ternary eutectic points although the liquidus temperature of the quaternary composition is lower than that of the ternary alloy composition.

Furthermore, the alloy composition of the present invention has a characteristic that it tends to easily form glassy phase (amorphous structure) without crystallization. The characteristic is so-called glass forming ability (GFA). Thus, it can be prepared as amorphous foil having a thin film shape through a rapid solidification method, e.g., melt-spinning. The amorphous foil is not fragile, differently from a crystallized structure. Moreover, it is mechanically flexible and its thickness can be controlled as thin as approximately 20 μm to approximately 80 μm. In Ti brazing, the thickness of filler foil controls the supply amount of filler metal, which decides the size of joint clearance. If the joint clearance is greater than a certain size, fragile inter-metal chemical compound is formed at the center of a brazing zone, which may lead to adverse influence on joint integrity. Therefore, it is advantageous to have the alloy composition a glass forming ability and form it in a thin film-shaped amorphous foil.

Hereafter, specific embodiments of the present invention will be described in detail. The following Examples are not restrictive but illustrative only.

EMBODIMENTS Examples 1 to 12 Zr—Ti—Ni Ternary Alloy

The following Table 1 shows Zr—Ti—Ni ternary alloy compositions prepared according to Examples 1 to 12 and Comparative Examples 1 to 8, constituent phases identified through X-ray diffraction analysis, and solidus temperature and liquidus temperature obtained through differential thermal analysis.

TABLE 1 Composition Solidus Liquidus (at. %) Constituent Phase Temperature Temperature Examples Zr Ti Ni Zr₂Ni (Zr,Ti)₂Ni Zr(Ti) (T_(s), ° C.) (T_(l), ° C.) Example 1 48 30 22 √ √ √ 798 813 Example 2 52 25 23 √ √ √ 798 815 Example 3 51 26 23 √ √ √ 798 809 Example 4 48 29 23 √ √ √ 798 812 Example 5 52 24 24 √ √ √ 798 811 Example 6 50 26 24 √ √ √ 798 809 Example 7 48 28 24 √ √ √ 798 815 Example 8 47 29 24 √ √ √ 798 818 Example 9 50 25 25 √ √ √ 798 820 Example 10 49 26 25 √ √ √ 797 817 Example 11 47 27 26 √ √ √ 798 825 Example 12 49 25 26 √ √ √ 797 825 Comparative 50 31 19 √ √ √ 796 850 Example 1 Comparative 46 33 21 √ √ √ 799 845 Example 2 Comparative 55 23 22 √ √ √ 798 842 Example 3 Comparative 53 22 25 √ √ √ 798 846 Example 4 Comparative 44 29 27 √ √ √ 798 847 Example 5 Comparative 45 22 28 √ √ √ 798 849 Example 6 Comparative 46 24 30 √ √ √ 798 858 Example 7 Comparative 43.9 22.8 33.3 √ √ — 850 869 Example 8

The ternary alloy compositions of the Examples 1 to 12 showed liquidus temperature not higher than approximately 825° C., specifically, ranging from approximately 809° C. to approximately 825° C. These temperatures are remarkably lower than those of Comparative Examples 1 to 8. The composition having the lowest liquidus temperature among the Examples was Zr₅₀Ti₂₆Ni₂₄ of Example 6.

It should be noted that the Examples 1 to 12 and Comparative Examples 1 to 7 have a solidus temperature ranging from approximately 796° C. to approximately 799° C., except for Comparative Example 8. This implies that their solidus temperature is closely related to the Ni content. In other words, when the Ni content was not more than approximately 30 at %, the solidus temperature of approximately 850° C. dropped drastically to a temperature lower than 800° C. This result proves that the alloy composition of the Comparative Example 8 and the alloy compositions of the Examples 1 to 12 and the Comparative Examples 1 to 7 belong to different eutectic systems.

Since the alloy composition of the Comparative Example 8, whose Ni content is approximately 33.3%, belongs to a pseudo binary Zr₂Ni—(Zr,Ti)₂Ni eutectic system, which is already known, it has a high solidus temperature of approximately 850° C. Since the alloy compositions of the Examples 1 to 12 and the Comparative Examples 1 to 7 whose Ni content is not more than approximately 30 at % belongs to a pseudo ternary eutectic system of Zr(Ti) solid solution phase, Zr₂Ni phase, and (Zr,Ti)₂Ni phase, they have a low solidus temperature lower than approximately 800° C.

Experimental Example 1 DTA of Ternary Alloy Composition According to the Present Invention

Differential thermal analysis (DTA) was performed on the Zr₅₀Ti₂₆Ni₂₄ alloy composition of the Example 6 based on heating and cooling cycle and the result was presented in FIG. 5.

FIG. 5 shows that only a single endothermic and exothermic peak appeared in the heating and cooling cycle, respectively, and the temperature difference (ΔT) between the peaks was as narrow as 11° C.

This result showed that the alloy composition of the Example 6 is the deepest eutectic point among the Zr—Ti—Ni ternary alloy compositions of the present invention.

Experimental Example 2 Observation of Microstructures of Ternary Alloy Compositions of the Present Invention and Alloy Compositions of the Comparative Examples and Comparison of their Constituent Phases

Samples were prepared by re-melting the Zr₅₀Ti₂₆Ni₂₄ alloy composition of the Example 6 and Zr_(43.9)Ti_(22.8)Ni_(33.3) alloy composition, which is an alloy composition at a pseudo eutectic point between a Zr₂Ni phase and (Zr,Ti)₂Ni phase of Comparative Example 8 illustrated in FIG. 4 re-melted and slowly solidified at a rate of 1° C./min in a vacuum furnace. FIGS. 7 (a) and 7(b) show Scanning Electron Microscope (SEM) images of the microstructure of the acquired samples.

As shown in FIG. 7( a), the alloy composition of the Example 6 has a typical eutectic structure formed of three constituent phases. Also, composition and crystal structure analysis using an X-ray diffraction (XRD) and a Transmission Electron Microscope (TEM) confirmed that the three phases were an α-Zr(Ti) solid solution phase (hcp), Zr₂Ni phase (bct), and (Zr,Ti)₂Ni phase (hcp) at room temperature.

Meanwhile, as shown in FIG. 7( b), the microstructure of the alloy composition of the Example 8 exhibited a typical eutectic structure formed of two constituent phases. The composition and crystal structure analysis using the XRD analysis of FIG. 4 and a TEM analysis revealed that the two constituent phases were Zr₂(Ni) phase (bct) and (Zr,Ti)₂Ni phase (hcp).

Examples 13 to 56 Zr—Ti—Ni—Cu Quaternary Alloy

The following Table 2 shows compositions of Zr—Ti—Ni—Cu quaternary alloys prepared according to Examples 13 to 56 of the present invention and Comparative Examples 9 to 24, their constituent phases analyzed through X-ray diffraction, and their solidus temperature and liquidus temperature obtained through differential thermal analysis.

TABLE 2 Composition Solidus Liquidus (at %) Cu/ Constituent Phase Temperature Temperature Examples Zr Ti Ni Cu (Ni + Cu) Zr₂Ni (Zr,Ti)₂Ni Zr(Ti) Zr₂Cu (T_(s,) ° C.) (T_(l,) ° C. ) Example 13 60 21 13 6 0.31 √ √ √ — 775 800 Example 14 57 24 13 6 0.31 √ √ √ — 774 791 Example 15 56 25 13 6 0.31 √ √ √ — 775 789 Example 16 53 28 13 6 0.31 √ √ √ — 775 800 Example 17 60 20 13 7 0.35 √ √ √ — 773 803 Example 18 59 21 13 7 0.35 √ √ √ — 775 792 Example 19 55 25 13 7 0.35 √ √ √ — 773 785 Example 20 58 21 14 7 0.33 √ √ √ — 775 786 Example 21 54 25 14 7 0.33 √ √ √ — 773 795 Example 22 57 21 14 8 0.36 √ √ √ — 774 785 Example 23 55 23 14 8 0.36 √ √ √ — 772 793 Example 24 53 25 14 8 0.36 √ √ √ — 774 796 Example 25 55 22 20 3 0.13 √ √ √ — 789 798 Example 26 55 22 17 6 0.26 √ √ √ — 776 785 Example 27 55 22 13 10 0.43 √ √ √ — 775 788 Example 28 55 22 15 8 0.34 √ √ √ — 773 785 Example 29 54 23 15 8 0.34 √ √ √ — 774 786 Example 30 55 21 15 9 0.37 √ √ √ — 774 785 Example 31 54 22 15 9 0.37 √ √ √ — 772 787 Example 32 54 22 18 6 0.25 √ √ √ — 778 790 Example 33 54 22 16 8 0.33 √ √ √ — 773 784 Example 34 53 23 15 9 0.37 √ √ √ — 774 787 Example 35 52 24 21 3 0.12 √ √ √ — 788 800 Example 36 50 26 21 3 0.12 √ √ √ — 788 806 Example 37 56 20 16 8 0.33 √ √ √ — 773 805 Example 38 55 21 16 8 0.33 √ √ √ — 774 784 Example 39 54 22 16 8 0.33 √ √ √ — 774 783 Example 40 52 24 16 8 0.33 √ √ √ — 773 793 Example 41 51 25 16 8 0.33 √ √ √ — 774 797 Example 42 50 26 16 8 0.33 √ √ √ — 773 807 Example 43 48 28 16 8 0.33 √ √ √ — 773 809 Example 44 54 22 12 12 0.50 √ √ √ — 775 802 Example 45 52 24 12 12 0.50 √ √ √ — 780 809 Example 46 50 26 12 12 0.50 — √ √ √ 792 809 Example 47 48 28 12 12 0.50 — √ √ √ 790 808 Example 48 55 20 16 9 0.36 √ √ √ — 773 799 Example 49 54 21 16 9 0.36 √ √ √ — 774 784 Example 50 54 21 17 8 0.32 √ √ √ — 774 784 Example 51 53 22 15 10 0.40 √ √ √ — 773 796 Example 52 51 24 15 10 0.40 √ √ √ — 773 791 Example 53 50 25 17 8 0.32 √ √ √ — 774 800 Example 54 52 20 18 10 0.35 √ √ √ — 772 794 Example 55 48 22 18 12 0.26 √ √ √ — 773 808 Example 56 50 20 18 12 0.33 √ √ √ — 773 807 Comparative 56 27 9 8 0.47 √ √ √ — 775 825 Example 9 Comparative 63 20 9 8 0.47 √ √ √ — 775 823 Example 10 Comparative 48 32 12 8 0.40 √ √ √ — 774 830 Example 11 Comparative 65 15 10 10 0.50 √ √ √ — 790 856 Example 12 Comparative 58 18 21 3 0.12 √ √ √ — 788 846 Example 13 Comparative 46 30 21 3 0.12 √ √ √ — 787 828 Example 14 Comparative 46 30 16 8 0.33 √ √ √ — 774 819 Example 15 Comparative 58 18 12 12 0.50 √ √ √ — 775 837 Example 16 Comparative 58 18 8 16 0.66 √ √ √ — 782 872 Example 17 Comparative 52 24 8 16 0.66 — √ √ √ 797 849 Example 18 Comparative 48 28 8 16 0.66 — √ √ √ 803 830 Example 19 Comparative 60 15 15 10 0.40 √ √ √ — 771 828 Example 20 Comparative 46 25 21 8 0.27 √ √ √ — 773 825 Example 21 Comparative 55 15 20 10 0.33 √ √ √ — 772 853 Example 22 Comparative 45 22 18 15 0.44 √ √ — √ 800 840 Example 23 Comparative 50 16.5 18.5 15 0.46 √ √ — √ 799 819 Example 24

The Zr—Ti—Ni—Cu quaternary alloy compositions of the present invention prepared according to the Examples 13 to 56 had a liquidus temperature under approximately 809° C. ranging from approximately 783° C. to approximately 809° C., which is considerably lower than those of the alloy compositions prepared according to the Comparative Examples 9 to 24. Among the alloy compositions of the Examples, Zr₅₄Ti₂₂Ni₁₆Cu₈ alloy of the Example 39 showed the lowest liquidus temperature, which was 783° C.

Referring to the Table 2 and the following Experimental Example 4, the quaternary alloys of the present invention were acquired by solidly dissolving Cu in the ternary alloy compositions of the present invention. Thus, it can be seen that the quaternary alloys includes a constituent phase of Zr(Ti) solid solution phase (hcp) with Cu dissolved therein, Zr₂Ni phase (bct) with Cu dissolved therein, and (Zr,Ti)₂Ni phase (hcp) with Cu dissolved therein, or a constituent phase of Zr(Ti) solid solution phase (hcp) with Cu dissolved therein, Zr₂Cu phase (bct) with Ni dissolved therein, and (Zr,Ti)₂Ni phase (hcp) with Cu dissolved therein.

A study, entitled “Non-Crystalline Solids,” Vol. 250-252, 1999, pp. 560-565, reports that Zr₅₀Ti_(16.5)Ni_(18.5)Cu₁₅ alloy composition of Comparative Example 24 has three constituent phases: Zr₂Ni (bct), (Zr,Ti)₂Ni (hcp), and Zr₂Cu (bct). The alloy composition of the Comparative Example 24 has a significant difference from the alloy compositions of the present invention in that it does not include Zr(Ti) solid solution phase. When the total amount of Ni and Cu (Ni+Cu) is not more than approximately 30 at %, the quaternary alloy compositions of the present invention and the alloy compositions of the Comparative Examples included Zr(Ti) solid solution phase as their constituent phase. Therefore, when the value obtained by summing the Ni content and the Cu content exceeds 30 at % as shown in the Comparative Examples 23 and 24, the constituent phase did not include Zr(Ti) solid solution phase. Thus their solidus temperature and liquidus temperature were decided to be high. When the ternary alloy compositions of the present invention including Ni not more than approximately 30 at %, a new type of eutectic alloy including the Zr(Ti) solid solution phase is formed, which leads to descending solidus temperature and liquidus temperature.

To be specific, referring to the Table 2, the constituent phases of the quaternary alloy compositions prepared according to the present invention included

Zr(Ti) solid solution phase (hcp) with Cu dissolved therein, Zr₂Ni phase (bct) with Cu dissolved therein, and (Zr,Ti)₂Ni phase (hcp) with Cu dissolved therein, or they included Zr(Ti) solid solution phase (hcp) with Cu dissolved therein, Zr₂Ni phase (bct) with Ni dissolved therein, and (Zr,Ti)₂Ni phase (hcp) with Cu dissolved therein. In short, the quaternary alloy compositions of the present invention are considered to have low solidus temperature not higher than approximately 792° C. due to the presence of Zr(Ti) solid solution and dissolution of Cu in each constituent phase. This solidus temperature is more than 8° C. lower than those of the Comparative Examples 23 and 24, which are as high as approximately 800° C.

Meanwhile, as the content of Cu in the Examples 46 and 47 is higher than those of the other examples, this results in the formation of the Zr₂Cu (bct), raising the solidus temperature somewhat higher than the compositions of the other Examples. Since the alloy compositions of the Examples 46 and 47 also included the Zr(Ti) solid solution phase, just as the other Examples do, it can be seen that they have relatively lower solidus and liquidus temperatures than those of the Comparative Examples. When the content of Cu exceeded approximately 12 at %, the liquidus was increased drastically, which is shown in the Comparative Examples 17 to 19, 23 and 24.

Experimental Example 3 DTA of Quaternary Alloy Compositions According to the Present Invention

Differential thermal analysis was carried out to the Zr₅₄Ti₂₂Ni₁₆Cu₈ of the Example 39 according to heating and cooling. The result was as shown in FIG. 6.

FIG. 6 shows that only a single endothermic and exothermic peak appeared in the heating curve and the cooling curve, respectively, and the temperature difference (ΔT) between the peaks was as narrow as 9° C. This result shows that the alloy composition of the Example 39 had the deepest eutectic point among the Zr—Ti—Ni—Cu quaternary alloy compositions prepared according to the present invention.

Experimental Example 4 Observation of Microstructure of Quaternary Alloy Compositions of the Present Invention and Comparison of Constituent Phases

The Zr₅₄Ti₂₂Ni₁₆Cu₈ alloy composition of the Example 39 was re-melted at a temperature over its melting point in vacuum and slowly solidified at a rate of 1° C./min to thereby produce a sample. FIG. 8 shows Scanning Electron Microscophic (SEM) images of the sample.

As shown in FIG. 8, the alloy composition of the Example 39 had a typical eutectic structure including three constituent phases. Composition and crystalline structure analysis through XRD and TEM revealed that the three constituent phases were Zr(Ti) solid solution phase (hcp) including Cu dissolved therein, Zr₂Ni phase (bct) with Cu dissolved therein, and (Zr,Ti)₂Ni phase (hcp) with Cu dissolved therein at room temperature. The three constituent phases included Cu up to its solubility limit, and there was no change in the type of constituent phases in comparison with ternary alloy composition of the present invention.

Experimental Example 5 XRD Analysis of Ternary and Quaternary Alloy Compositions Prepared Through Melt-Spinning According to the Present Invention

XRD analysis was performed onto samples prepared by melt-spinning ternary and quaternary alloy compositions of the present invention in the form of foil. The results were presented in FIGS. 9 and 10, respectively. FIGS. 9 and 10 showed that the ternary and quaternary alloy compositions of the present invention had a glass forming ability that was proved by diffuse hallow pattern from XRD analysis due to their amorphous structure, and they were easily formed into amorphous foil through the melt-spinning.

Experimental Example 6 Tensile Strength Test at Room Temperature Based on Brazing Heat Cycle of Joint Body Using Alloy Composition of the Present Invention as Filler Alloy

A joint body was manufactured using Ti-6Al-4V having strength of approximately 1040 MPa as base metal and the Zr₅₄Ti₂₂Ni₁₆Cu₈ alloy composition of the Example 39 as filler alloy and brazing them at a joining temperature of approximately 800° C. to approximately 950° C. for 60 minutes. Also, tensile strengths of the base metal (Ti-6Al-4V) without joint were tested at room temperature after exposing only the base metal to the same brazing heat cycle.

The tensile strengths of the joint body and the base metal at room temperature obtained from the test are presented in FIG. 11. In FIG. 11, the tensile strength of the base metal is the maximum tensile strength and the tensile strength of the joint body is rupture strength. FIG. 11 shows that the higher the heat cycle temperature becomes, the lower the maximum tensile strength of the base metal grows. Thus, the tensile strength of the joint body is decreased, too. The tensile rupture of the joint body occurred at a joint under all joining conditions. According to the test result, when the brazing temperature was high, the strength of the base metal was decreased and the joining strength became low, too. The joint strength of the joint body brazed at approximately 800° C., which is the lowest temperature, is 965 MPa, which is the closest to the strength (1040 MPa) of the base metal before the thermal exposure.

Consequently, the present invention lowers the brazing temperature to approximately 800° C. by using a filler alloy having a low melting point, minimizes a decrease in the mechanical properties of Ti base metal and maximizes the mechanical characteristic of the joint body from the brazing heat cycle. 

What is claimed is:
 1. A Zr—Ti—Ni—Cu quaternary alloy composition, expressed as: Zr_(a)Ti_(b)Ni_(c)Cu_(d)  Formula 2 where a, b, c and d denote atomic % of Zr, Ti, Ni and Cu respectively; 48≦a≦60; 20≦b≦28; 19≦c+d≦30; 3≦d≦12; and 0.12≦d/(c+d)≦0.5, wherein constituent phase of the alloy composition at room temperature includes three phases, which are Zr₂Ni phase with Cu dissolved therein, (Zr,Ti)₂Ni phase with Cu dissolved therein, and Zr(Ti) solid solution phase with Cu dissolved therein, or which are Zr₂Cu phase with Ni dissolved therein, (Zr,Ti)₂Ni phase with Cu dissolved therein, and Zr(Ti) solid solution phase with Cu dissolved therein.
 2. The Zr—Ti—Ni—Cu quaternary alloy composition of claim 1, wherein liquidus temperature of the alloy composition ranges from approximately 783° C. to approximately 809° C.
 3. The Zr—Ti—Ni—Cu quaternary alloy composition of claim 1, wherein solidus temperature of the alloy composition ranges from approximately 772° C. to approximately 792° C. 